Preparation and properties of diphtheria toxoids in submerged culture. III. Development of a new semisynthetic medium

A new medium has been developed which does not contain any meat digest products and is suitable for the deep-culture production of high-potency diphtheria toxins. The main ingredient is a commercially available, tryptic digest of casein known as N.Z. Amine type A. It has been found that when the iron, calcium, and phosphate levels in the medium are carefully controlled by suitable additions of ferrous sulphate, calcium chloride, and inorganic phosphate solutions, high levels of diphtheria toxin are regularly produced (200 Lf/ml in a 48-hour growth period).